Chromosome instability (and resulting aneuploidy) has been recognized as a hallmark of cancer cells, and contributes to tumor progression by facilitating the genetic alterations required for acquisition of malignant phenotypes. Numerous studies have shown the frequent occurrence of abnormal amplification of centrosomes (generation of more than two centrosomes) in almost all types of solid tumors and certain types of lymphoma and leukemia, and the strong association between occurrence of centrosome amplification and aneuploidy. The detrimental consequence of centrosome amplification is prominently featured during mitosis: the presence of multiple centrosomes (spindle poles) results in mitotic defects, leading to an increased frequency of chromosome segregation errors. Indeed, centrosome amplification is now widely accepted as one of the major factors that contribute to chromosome instability in cancer. Centrosome amplification is caused primarily by uncontrolled duplication of centrosomes in a single cell cycle. We have recently found that ROCK II (Rho-associated kinase) localizes to centrosomes, and acts as a key regulatory protein for the initiation of centrosome duplication in association with nucleophosmin (NPM/B23). NPM/B23 is one of the major targets of CDK2-cyclin E, which plays a key role in initiating centrosome duplication. CDK2-cyclin E-mediated phosphorylation renders NPM/B23 a higher binding affinity to ROCK II, and ROCK II becomes super- activated by NPM/B23 binding. ROCK II then promotes the initiation of centrosome duplication in a centrosome localization- and kinase activity-dependent manner. ROCK II activation is also controlled by binding to an activated Rho protein (Rho-GTP), a major signal transducer downstream of many growth factor receptors (receptor tyrosine kinases/RTKs). These observations put forward to a model, in which two pathways (CDK2-NPM/B23 pathway and RTK-Rho-ROCK II pathway) converge by the physical interaction between ROCK II and NPM/B23 and super-activation of ROCK II to initiate centrosome duplication. In this research proposal, we will molecularly dissect the how ROCK II is controlled by these cancer-associated proteins to drive centrosome duplication, and how ROCK II controls centrosome duplication through focusing of the protein called LASP1, which we have recently identified as a potential centrosomal target of ROCK II for the initiation of centrosome duplication. Based on the facts that centrosome duplication occurs only in proliferating cells, and centrosome amplification is the major cause of chromosome instability in cancer, centrosome duplication and centrosome amplification can be effective targets for the cancer intervention protocols. Our research proposal that aim to understand the molecular mechanisms of the regulation of centrosome duplication and induction of centrosome amplification will provide vital information on this regard. PUBLIC HEALTH RELEVANCE: Cancer is the result of accumulation of many genetic alterations. Gain or loss of chromosomes (chromosome instability), which occurs frequently in cancer, introduces many genetic alterations simultaneously, hence accelerating tumors to acquire further malignant characteristics. In this research grant application, we will examine the mechanisms of how various oncoproteins and tumor suppressors, which are frequently mutated in cancer, maintain the integrity of chromosomes via controlling the duplication of centrosomes. The centrosome plays a critical role in the accurate segregation of chromosomes to two daughter cells during mitosis. Mutations of those oncoproteins and tumor suppressor proteins result in numeral abnormality of centrosomes, leading to mitotic defects and consequentially destabilization of chromosomes. As centrosome duplication occurs in actively proliferating cells such as cancer cells, centrosome duplication can be an effective target of cancer intervention, and the findings from our proposed studies will provide critical information on the development of superior cancer intervention protocols targeting centrosomes and cancer-associated proteins that control centrosome duplication.